The invention relates to a hybrid inflator composing at least one combustion chamber in which a propellant charge is arranged and which includes a discharge end, the propellant charge being formed of at least one propellant element, in accordance with the preamble of claim 1. Furthermore, the invention relates to a vehicle safety system comprising said hybrid inflator. The invention also relates to a method of forming a shock wave.
A hybrid inflator of the afore-mentioned type is known, for example, from DE 10 2013 018 886 A1. A bursting membrane divides the shown inflator housing into a combustion chamber and a gas supply chamber. The gas supply chamber is filled with gas, especially cold gas such as argon, helium or any other suitable gas mixture, and is closed to be pressure-tight by a bursting disk on the inflator end side. When activating the inflator, the igniter receives an electric signal to activate the same and, resp., to ignite the propellant. The ignition of the propellant provided in the combustion chamber results in sudden pressure increase in the combustion chamber so that the bursting membrane is destroyed or is abruptly opened and a large opening related to the diameter of the housing is formed in the bursting membrane. This abrupt opening generates a shock wave entering the gas supply chamber and passing through the same up to the bursting disk, with the bursting disk being opened.
The shock wave formed by opening the bursting membrane is intended to safeguard robust opening of the end-side bursting disk. In order to always achieve this with particular designs of hybrid inflators the measure so far has been to increase the combustion chamber pressure by increasing the bursting pressure of the bursting membrane. The shock wave generated in this way is sufficient to open also large hybrid inflators, for example. This requires massive reinforcement of the combustion chamber wall thicknesses, however, which have to be designed in accordance with a higher combustion chamber pressure. In the case of inflators in which the igniting unit initiates the shock wave, the pressures in the igniter chamber thus have to be appropriately high so as to generate a robust shock wave. This can be achieved by increasing the amount of propellant charge and/or also by highly charged igniters which themselves include an increased amount of pyrotechnics already and thus are very expensive.